Recently, as represented by cloud computing, a system configuration has been widely used in which a plurality of servers and a plurality of storage devices are installed at a data center and various services are provided to clients. In such a system configuration, an FC switch (fibre channel switch) that achieves high-speed communications is used to connect a plurality of servers to a plurality of storages.
A modern FC switch has a function whereby it stops the operation of a port temporarily when the port receives a predetermined number of invalid signals. This function prevents the FC switch from recursively repeating a link initialization process or linkup that is executed automatically after a link down is detected, thereby preventing a perpetual resource shortage.
More particularly, even when the operating system (OS) is shut down, if power is supplied to a server or storage device, the server or storage device may continue issuing optical signals to a switch. Because the driver is stopped but the adapter is not stopped, the adapter continues issuing optical signals to the switch. The issued optical signals are, because of a feature of the protocol, invalid signals having a meaningless value. As long as the switch is receiving invalid signals, the switch repeats processes to check the synchronization between signals, processes to tune the transmission rate, etc; therefore, a perpetual resource shortage occurs in the CPU (Central Processing Unit). The abovementioned function of temporarily stopping the port is used as a means of preventing such resource shortages.
Patent document 1: International Publication Pamphlet No. WO 2008/075425
A problem with the conventional technology is that the link initialization process is not stable. This problem occurs with not only an FC switch but also various other switches, such as an FCoE (Fibre Channel over Ethernet (registered trademark)) switch and an Ethernet (registered trademark) layer-2 switch.
Suppose, for example, that a switch temporarily stops a port when a server or the like that is connected to the switch is rebooted for a maintenance operation. After the reboot of the server or the like is completed, it starts a link-up process to link to the switch; however, because the port is stopped, the switch may not start the link-up process. Even if the server is rebooted as a purposive action, in other words, the reboot of the server is a normal action, the switch stops the port temporarily because it keeps receiving invalid signals.
Therefore, until a maintenance person disconnects and then reconnects the cable that is connected to the port from the switch, the switch may not start the link initialization process of linking the port to the server. As described above, in some cases, depending on the timing when a switch temporarily stops a port, the link initialization process may not start automatically; therefore, the link initialization process performed by such a switch may not be said to be stable. Moreover, with a large system having a plurality of servers, it is not practical for a maintenance person to disconnect and then reconnect cables to ports.